Combinations of zinc pyrithione and cuprous oxide are known to be excellent antifouling agents when formulated into paints and paint bases (i.e., the paint before pigment addition) also containing rosin, as disclosed, for example, in U.S. Pat. No. 5,057,153. Unfortunately, however, such paints have now been found to thicken or gel unacceptably within a few days, at best, or a few hours, at worst, when formulated with typical commercial grades of zinc pyrithione in combination with cuprous oxide.
Heretofore, various solutions to the problem of gellation of paints containing rosin and zinc pyrithione in combination with cuprous oxide, have been suggested. Illustrative solutions have been to use rigorously purified zinc pyrithione, as disclosed in U.S. Pat. No. 5,098,473, or to add amines or esterified rosin, as disclosed in U.S. Pat. No. 5,112,397, or to use a metal salt of rosin, as disclosed in U.S. Pat. No. 5,137,569. Since these solutions may have drawbacks such as increased cost or lack of compatibility with some paints, a new, economical solution to the problem would be highly desired by the paint manufacturing community in order to maximize flexibility in using this combination of biocides in view of its excellent biocidal activity.
The present invention provides one solution to this problem. Although individually cuprous oxide, 2,2'-dithiobis(pyridine-1-oxide) (hereinafter also referred to as "bispyrithione"), and its metal salt adducts and their hydrates are all known biocides, the use of a combination of bispyrithione or its metal salt adducts or their hydrates plus cuprous oxide as biocides in the production of a paint which is stable against gellation during storage have not been known heretofore to the knowledge of the present inventors.